Reactive oxygen species (ROS) produced by polymorph nuclear leukocytes (PMNs) and endothelial cells (ECs) during the innate immune response against invading pathogens are of major importance in governing PMN capture and extravasation at a site of infection. Although we have demonstrated the involvement of the transient receptor potential melastatin (TRPM) channel 2 (TRPM2) in mediating oxidant-induced calcium entry and loss of the endothelial barrier integrity in endothelial cells (ECs), the functio of the TRPM2 channel in ROS-induced trans endothelial migration of PMNs have not been assessed. Our studies suggest that TRPM2 functions in response to ROS to activate vascular PMN extravasation in infected lungs. We will thus test the hypothesis that the increase in lung micro vessel PMN transmigration and clearance of the bacterial pathogens from the infected lungs depend on the activation of endothelial TRPM2 by oxidants. To test this hypothesis we will follow the three specific aims: Aim #1 will address the requirement of the endothelial cell-TRPM2 channel in mediating transendothelial migration of PMNs at sites of bacterial infection, thereby promoting clearance of the invading pathogen from the lung. The proposed studies will use a transgenic mouse model expressing endothelial cell- restricted deletion of TRPM2 and mouse lung endothelia transduced with TRPM2 crispr/Cas9-gRNA to address the role of TRPM2 activation in the mechanism of increased lung PMN transmigration. We will establish the functional significance of TRPM2 in signaling PMN activation-induced lung PMN infiltration and bacterial clearance in a murine model of Pseudomonas aeruginosa pulmonary infection. Aim #2 will address whether PMN-activated TRPM2 plays a critical role during bacterial infection by distributing P-selecting on the EC surface, and recruiting PMNs to the site of infection. Specifically, we will determine whether TRPM2-regulated Ca2+ entry induces P-selectin mobilization to EC surface through activation of PKCa signaling. Aim #3 will address the signaling mechanisms by which PMN-induced activation of TRPM2 in ECs mediates formation of vascular interendothelial gaps and PMN transendothelial migration. The studies will establish the role of TRPM2-regulated Ca2+ signaling in ECs in promoting disassembly of Adherens Junctions complexes through phosphorylation of the vascular endothelial (VE)-cadherin, resulting in loss of endothelial cell-cell adhesion and thereby mediating PMN transmigration. Overall, these studies will establish the functional significance of TRPM2 in the induction of PMN transendothelial migration, which is necessary for host defense against bacterial infections; therefore, manipulating TRPM2 function in the endothelium represents a novel target to mount effective host's immunity against pulmonary gram-negative infection.